1. Field of the Invention
The present invention relates to a control system and method for a hybrid vehicle driven by an engine and a motor, and in particular, relates to a technique for controlling the amount of power assistance when the output of the engine is assisted using the motor.
2. Description of the Related Art
Conventionally, hybrid vehicles employing an engine and a motor as driving sources are known. Among them, in parallel hybrid vehicles, the motor is used as an assistance driving source for assisting the output of the engine. More specifically, when such a parallel hybrid vehicle is accelerated, the engine output is assisted by driving the motor, and when decelerated, various controls, such as battery charging using deceleration regeneration, are performed so as to maintain necessary electrical energy of the battery (i.e., the necessary remaining charge) and also to satisfy the driver""s intention.
In such hybrid vehicles, Japanese Unexamined Patent Application, First Publication No. 2001-61204 discloses an assistance control system for hybrid vehicles, in which the assistance mode, in which the output of the engine is assisted using the motor, is divided into a plurality of modes to which different control processes are assigned according to the driving state of the vehicle, and one of the modes is selected based on the motor output (i.e., the amount of power assistance) of each mode or the like.
In the above-explained conventional hybrid vehicles, when the amount of power assistance assigned to each mode (in the assistance mode) is considerably different (i.e., the difference between the amounts of assistance of different modes is great), the change in the amount of assistance at the mode change is great, so that passengers in the vehicle may feel that the acceleration has suddenly changed.
In particular, when the assistance mode is switched from a mode having a relatively small amount of power assistance to a mode having a relatively large amount of power assistance, a discontinuity (i.e., a sudden change) is produced in the torque, which the passengers have not anticipated, thereby degrading driving performance.
In consideration of the above circumstances, an object of the present invention is to provide a motor output control system and method effectively used when changing the assistance mode in which the output of the internal combustion engine is assisted by using the motor, so as to prevent a sudden change in the passengers"" feeling for the acceleration and to secure smooth acceleration performance.
Therefore, the present invention provides a motor output control system built in a hybrid vehicle which comprises an internal combustion engine (e.g., an engine E in an embodiment explained below) and a motor (e.g., a motor M in the embodiment explained below) as driving sources and in which the output of the internal combustion engine is assisted using the motor according to the driving state of the vehicle, the system comprising:
an assistance mode determination section (which may be provided in a motor ECU 1 in the embodiment explained below) for determining whether the output assistance using the motor is permitted with respect to each of different control modes for the output assistance, where the determination is performed according to the driving state of the vehicle;
an amount of assistance calculating section (which may be provided in the motor ECU 1 in the embodiment explained below) for calculating an amount of output assistance for each of the different control modes (e.g., the starting assistance command value STRAST, the scramble assistance command value SCRAST, the WOT assistance command value WOTAST, and the ECO assistance command value ECOAST in the embodiment explained below);
an assistance permitting section (which may be provided in the motor ECU 1 in the embodiment explained below) for permitting the output assistance using the motor when the output assistance is permitted in any control mode according to the determination of the assistance mode determination section;
an amount of assistance selecting section (which may be provided in the motor ECU 1 in the embodiment explained below) for selecting the maximum amount of assistance among the amounts of assistance, which are calculated by the amount of assistance calculating section and are assigned to the different control modes, when the output assistance using the motor is permitted by the assistance permitting section; and
a mode shift section (which may be provided in the motor ECU 1 in the embodiment explained below) for:
comparing a previous value of the maximum amount of assistance (e.g., the final acceleration assistance command value ACCASTF in the embodiment explained below), selected by the amount of assistance selecting section last time, with the current value (e.g., the acceleration assistance command value ACCAST in the embodiment explained below) of the maximum amount of assistance selected this time;
calculating a shift value (e.g., xe2x80x9cACCASTFxe2x88x92#DACCASTMxe2x80x9d in the embodiment explained below) obtained by subtracting a predetermined assistance value (e.g., the predetermined assistance command subtraction value #DACCASTM in the embodiment explained below) from the previous value when the current value is less than the previous value; and
setting the amount of assistance using the motor to the shift value until the shift value becomes equal to or less than the current value, so as to gradually shift the amount of assistance from the previous value to the current value.
According to the above system, when the control mode for motor assistance is changed according to the driving state of the vehicle, if the amount of assistance selected this time is less than the amount of assistance selected last time, the mode shift section sets the amount of assistance of this time to a value obtained by subtracting a predetermined assistance value from the previous value.
That is, when the amount of assistance is changed according to a control mode change for the assistance, the mode shift section sets the amount of assistance in a manner such that the amount of assistance gradually shifts to the amount corresponding to a value assigned to the newly-selected control mode, without simply switching the amount of assistance from the previous value assigned to the previous mode to the newly-selected value. Accordingly, the amount of assistance can be smoothly changed, thereby preventing a sudden change in the feeling of acceleration of the passengers in the vehicle and securing smooth acceleration and driving performance.
The assistance permitting section may include the assistance mode determination section. That is, when the assistance permitting section determines whether the output assistance using the motor is performed (i.e., permitted), the assistance mode determination section determines whether the output assistance using the motor is permitted with respect to each of the different control modes for the output assistance, thereby selecting permittable control modes.
As a typical example, the control modes for the output assistance using the motor include at least:
a starting assistance mode (e.g., the starting assistance in the embodiment explained below) for performing the output assistance when the vehicle is started;
a sudden acceleration assistance mode (e.g., the scramble assistance in the embodiment explained below) for performing the output assistance when the vehicle is suddenly accelerated;
a low load assistance mode (e.g., the ECO assistance in the embodiment explained below) for performing the output assistance when the load of the internal combustion engine is low; and
a high load assistance mode (e.g., the WOT assistance in the embodiment explained below) for performing the output assistance when the load of the internal combustion engine is high.
Accordingly, the amount of power assistance can be gradually changed when the assistance mode is switched, for example:
(i) when the acceleration is performed after the mode is switched to the low load assistance mode, in which output assistance is performed in a low load state of the internal combustion engine, or to the high load assistance mode, in which output assistance is performed in a high load state of the internal combustion engine, after the starting assistance mode (in which the output assistance is performed when the vehicle is started) is terminated, or
(ii) when acceleration is performed by switching the acceleration mode to the low load or high load assistance mode after termination of the sudden acceleration assistance mode in which the output assistance is temporarily performed when the vehicle is suddenly accelerated.
Therefore, when the control mode is changed, a sudden change in the feeling of acceleration of the passengers in the vehicle can be prevented, thereby securing smooth acceleration and driving performance.
The present invention also provides a motor output control method used for a hybrid vehicle which comprises an internal combustion engine and a motor as driving sources and in which the output of the internal combustion engine is assisted using the motor according to the driving state of the vehicle, the method comprising:
an assistance mode determination step of determining whether the output assistance using the motor is permitted with respect to each of different control modes for the output assistance, where the determination is performed according to the driving state of the vehicle (refer to steps S104, S108, S109, S111, and S112 in an embodiment explained below);
an amount of assistance calculating step of calculating an amount of output assistance for each of the different control modes (refer to steps S312 to S315 in the embodiment explained below);
an assistance permitting step of permitting the output assistance using the motor when the output assistance is permitted in any control mode according to the determination in the assistance mode determination step (refer to steps S101 to S114 in the embodiment explained below);
an amount of assistance selecting step of selecting the maximum amount of assistance among the amounts of assistance, which are calculated in the amount of assistance calculating step and are assigned to the different control modes, when the output assistance using the motor is permitted in the assistance permitting step (refer to steps S319 to S330 in the embodiment explained below); and
a mode shift step (refer to steps S331 to S339 in the embodiment explained below) of:
comparing a previous value (e.g., the final acceleration assistance command value ACCASTF in the embodiment explained below) of the maximum amount of assistance, selected in the amount of assistance selecting step last time, with the current value (e.g., the acceleration assistance command value ACCAST in the embodiment explained below) of the maximum amount of assistance selected this time;
calculating a shift value (e.g., xe2x80x9cACCASTFxe2x88x92#DACCASTMxe2x80x9d in the embodiment explained below) obtained by subtracting a predetermined assistance value (e.g., the predetermined assistance command subtraction value #DACCASTM in the embodiment explained below) from the previous value when the current value is less than the previous value; and
setting the amount of assistance using the motor to the shift value until the shift value becomes equal to or less than the current value, so as to gradually shift the amount of assistance from the previous value to the current value.